Modelling fuel combustion in iron ore sintering

In an iron ore sintering bed, the combustion behaviour of coke particles together with velocity of the flowing gas stream determines the temperature, width and speed of the traversing flame front. A bed heat treatment mathematical model was formulated in an earlier study to describe this complex relationship. An area of improvement in the model is the description of the coke combustion process, which is highly dependent on the resistances controlling the flow of gases to and from the coke particles. These vary for different coke particles because of the prior coarsening of the sinter mix by granulation. The characteristic structure of granules – nuclear particle with an adhering fines layer – indicates that gases have better access to finer coke particles. In this study, an available granulation model is integrated into the heat treatment model to provide a novel description of coke positioning within granules. In addition to this change, two endothermic reactions were introduced into the model. Using the previous and modified models, predicted bed temperature–time profiles as a function of position down the bed, were compared against embedded thermocouples results from seventeen laboratory sinter tests. Generally, the modified definition of coke combustion behaviour resulted in improved comparison with experimental results. In the sintering literature, studies have been reported on: the use of charcoal/biomass char to replace coke, the preferential placement of coke particles on the outside of granules, and varying the size distribution of the coke particles. Improving the access of gases to coke particles and decreasing coke size are comparable to using more reactive fuels. Combustion rate, efficiency and flame front properties are all influenced by fuel reactivity. Model predictions of changes in bed temperatures, flame front properties and sintering performance caused by fuel type, location and size are consistent with reported observations.